The present invention generally relates to air cycle environmental control systems and, more particularly, to 2 spool air cycle systems.
Environmental control systems (ECSS) are used to provide a supply of conditioned air to an enclosure, such as an aircraft cabin, cockpit and avionics equipment cooling (air and liquid). In the past, an air cycle ECS has typically operated on a flow of bleed air taken from an intermediate or high-pressure stage within a jet engine having multi-compression stages. The bleed air has usually been pre-cooled within a primary heat exchanger with heat being dumped to RAM air and then flowed to a compressor. After compression, the air has been routed through a series of heat exchangers and condensers. Then, the air has typically been expanded by a turbine, which is mechanically engaged to the compressor. Finally, the air is conditioned to supply temperature and ready to delivery for compartment and equipment cooling.
Past air cycle ECS designs have included 2, 3 and 4 wheel bootstrap designs. The general distinction among the three designs relates to the number of so-called wheels, which are mechanically engaged to one another. All three of the bootstrap designs typically utilize a reheater and a condenser heat exchanger to respectively pre-cool the bleed air and then condense the water vapor in it. After condensation, the condensed water is removed by a water extractor. The resulting dehumidified air flows to the reheater where the remaining water droplets are evaporated, leaving the residual moisture in the vapor phase. The dry air then flows to a turbine for expansion and consequent cooling. The expansion will typically cool the air to below freezing temperature and thus the vapor particles form ice nuclei and crystallize into snow, which are swept downstream.
In the conventional 2-wheel bootstrap air cycle system, the subfreezing expanded air from the turbine can be used to absorb waste heat from the liquid cooling system then is supplied to cool the air load and the cabin. In order to maintain the air load and cabin air supply temperatures to the design requirement (normally 35xc2x0 F.) as well as satisfying the liquid supply temperature, additional air flow, beyond the flow schedule for the cabin and air cooled load, is required. However, the additional air flow, can generally be used for regenerative cooling to enhance system performance, the regenerative flow is discharged to ambient. This extra flow demand from the bleed source (i.e., an aircraft engine) imposes a penalty to the aircraft""s overall performance.
Considering the shortcomings of the presently available 2-wheel bootstrap air cycle systems, there is a need for an advanced air cycle system which increases overall performance of an aircraft by consuming less bleed air and providing an efficient heat sink condition.
In one aspect of the present invention, an integrated environmental control system for providing conditioned air supply in an aircraft comprises a first compressor and a first turbine of a first air cycle system as well as a second turbine and a second compressor of a second air cycle system.
The first compressor receives a first air flow from an engine of the aircraft and transforms the first air flow into a first compressed air flow. The first turbine is mechanically connected to the first compressor. The first turbine transforms the first compressed air flow into a first expanded air flow while simultaneously cooling the first compressed air flow and converting the energy of the first compressed air flow into a first work output to rotationally drive the first compressor.
The second turbine of the second air cycle system receives the first expanded air flow and transforms it into a second expanded air flow while simultaneously cooling the first expanded air flow and converting the energy of it into a second work output. The second compressor is in fluid communication with the second turbine and driven by the second work output. The second compressor receives the second expanded air flow from the second turbine through an air flow path. The second expanded air flow in the air flow path absorbs thermal energy from the first air cycle system.
In another aspect of the present invention, a process for supplying conditioned air in an aircraft comprises the steps of receiving a bleed air flow from an engine of the aircraft, transforming the bleed air flow into a first compressed air flow in a compressor of a bootstrap air cycle system, transforming the first compressed air flow into a first expanded air flow in a turbine of the bootstrap air cycle system, transforming the first expanded air flow into a second expanded air flow by a turbine of a regenerative air cycle system and receiving the second expanded air flow through a second compressor of the regenerative air cycle system.
The first compressed air flow is transformed into a first expanded air flow by utilizing a first turbine of the bootstrap air cycle system while simultaneously cooling the first compressed air flow and converting the energy of the first compressed air flow into a first work output to rotationally drive the first compressor. The first expanded air flow is transformed into a second expanded air flow by utilizing a second turbine of the regenerative air cycle system while simultaneously cooling the first expanded air flow and converting the energy of the first expanded air flow into a second work out put. The second expanded air flow is received through a second compressor of the regenerative air cycle system. The second compressor is in fluid communication with the second turbine and rotationally driven by the second work output. The second compressor receives the second expanded air flow from the second turbine through an air flow path. The second expanded air flow in the air flow path absorbs thermal energy from the bootstrap air cycle system through a regenerative heat exchanger.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.